Light Source Modulation for a Scanning Microscope

ABSTRACT

Systems, method, and non-transitory computer readable medium for imaging an object. The system includes a scanner. The scanner positions a spot of light from a light source on the object along a scanning path. The scanning path includes a plurality of scan lines. The spot moves along the scanning path at a scanning velocity. The scanning velocity is not constant. The intensity of the spot of light is modulated as a function of the scanning velocity. The system includes a detector that is arranged to output data associated with positions along the scanning path. The system includes one or more processors that perform calculations. Pixels are calculated based on the output data. The image is constructed of the object based on the pixels.

BACKGROUND

1. Field of Art

The present disclosure relates to a scanning imaging system, methods,and non-transitory computer readable medium with instructions formodulating a light source.

2. Description of the Related Art

Laser confocal microscopes and Scanning Laser Ophthalmoscopes (SLO),obtain a two dimensional images of a specimen by employing two scannersto dynamically update positions of a laser spot on the specimen. The twoscanners are a resonant scanner and a linear scanner. The resonantscanner, also called the “fast scanner” oscillates back and forth at kHzrates to update the position of the laser spot in a first direction(e.g., X direction in Cartesian coordinates). The linear scanner, alsocalled the “slow scanner” oscillates back and forth at Hz rates toupdate the position of the laser spot in a second directionperpendicular to the first direction (e.g., Y direction in Cartesiancoordinates). The two scanners work together to sweep the laser spotacross a portion of the specimen being imaged (scanning area), producinga two dimensional image of the specimen. The fast scanner is typicallydriven by a sinusoidal signal (or a similar such signal) to achievehigh-speed scanning hence its physical motion is also sinusoidal or veryclose to sinusoidal. The slow scanner is driven by a periodic rampsignal or saw-tooth signal.

One of the consequences of using a resonant scanner is that the scanningspeed at the center of the scanning area is much faster than thescanning speed at the edge of the scanning area. In the prior art theintensity of the laser spot before it enters the scanner is keptconstant before it enters the scanner. Thus, the radiant flux (radiantenergy per unit time) is greater at the edges than at the center.

The light reflected from the specimen is detected by a photo detectorsuch as a Photo Multiplier Tube (PMT) or an Avalanche Photo Diode (APD),and the detected signal from the detector is converted by anAnalog/Digital converter (ADC) to a digital signal. The detected signalstrength is proportional to the intensity of the illumination light atthe specimen. When measuring the relative intensity with the detector,the detector is calibrated relative to the intensity of the illuminationlight received by the specimen. In order to minimize calibration errorthe measurement window is limited to a central area of the scanning areain which the scanning speed is substantially constant. Thus, theillumination light at the specimen in the measurement window isrelatively constant. The detected signals are then truncated andreshaped according to the scanner movement in order to obtain a finalimage.

When the specimen is a human eye, laser safety is an important issue.Scanning Laser Ophthalmoscopes are designed to be in compliance withANSI Z136 Laser Safety Standards, thus the radiant flux received by theeye during the measurement process is kept below a maximum intensity. Ifthe source intensity is kept constant then the source intensity islimited to the light received at the edges of the scanning window.Alternatively, the light source is modulated so that the light source isOFF at the edges of the scanning window and is only ON during or aroundthe measurement window.

Some scanning projectors include systems in which light passes throughan optical filter that variably attenuate the light beam as function ofposition. These systems are inappropriate for imaging systems in whichthe intensity of light source should be dynamically adjustable tocompensate for the dynamic variability of the imaging system.

Sometimes it is better to use non-constant source illumination so thatthe specimen receives uniform illumination. When the specimen receivesuniform illumination than the thermal and photochemical effect of theillumination on the specimen is also uniform. The existing technologiesmodulate the detection laser using only two states, ON/OFF. Thus, thewhole scanning area is not used for imaging because edges of the areaare not illuminated.

SUMMARY

System, method, and non-transitory computer readable medium for imagingan object. The system includes a scanner. The scanner positions a spotof light from a light source on the object along a scanning path. Thescanning path includes a plurality of scan lines. The spot moves alongthe scanning path at a scanning velocity. The scanning velocity is notconstant. The intensity of the spot of light is modulated as a functionof the scanning velocity. The system includes a detector that isarranged to output data associated with positions along the scanningpath. The system includes one or more processors that performcalculations. Pixels are calculated based on the output data. The imageof the object is constructed based on the pixels.

An aspect of at least one exemplary embodiment comprises an externalmodulator for modulating the light source. An aspect of at least oneexemplary embodiment comprises directly modulating the light source.

An aspect of at least one exemplary embodiment comprises calculating thepixels by integrating the intensity of the detected light.

In an aspect of at least one exemplary embodiment the intensity of thespot of light is modulated as a function of the average scanningvelocity.

In an aspect of at least one exemplary embodiment the average scanningvelocity is averaged over a period equal to the pixel clock time.

In an aspect of at least one exemplary embodiment the intensity of thespot of light is modulated as function of the scanning velocity during afirst window, and the intensity of the spot of light is substantiallyzero outside of the first window.

In an aspect of at least one exemplary embodiment the scanner is aresonant scanner that positions the spot of light with sinusoidalmotion. Constructing the image comprises correcting image distortioncaused by the sinusoidal motion by integration.

An aspect of at least one exemplary embodiment is an imaging method forimaging an object. The imaging method comprises scanning a spot of lightfrom a light source on the object along a scanning path. The scanningpath includes a plurality of scan lines. The spot moves along thescanning path at a scanning velocity. The scanning velocity is notconstant. The intensity of the spot of light is modulated as a functionof the scanning velocity. The output data associated with positionsalong the scanning path is detected. Pixels are calculated based on theoutput data. An image is constructed of the object based on the pixels.

An aspect of at least one exemplary embodiment is a non-transitorycomputer readable medium encoded with instructions for imaging anobject. The instructions include sending instructions to a scanner toscan a spot of light from a light source on the object along a scanningpath. The scanning path includes a plurality of scan lines. The spotmoves along the scanning path at a scanning velocity. The scanningvelocity is not constant. The instruction includes sending instructionsto modulate the intensity of the spot of light as a function of thescanning velocity. Receiving output data from a detector. The outputdata is associated with positions along the scanning path. Calculatingpixels based on the output data. Constructing an image of the objectbased on the pixels.

Further features and aspects will become apparent from the followingdetailed description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments.

FIG. 1 is an illustration of an ophthalmoscope.

FIGS. 2A-D are illustrations of scanning position, velocity andintensity.

FIGS. 3-4 are illustrations of areas blocked by a modulator.

FIGS. 5A-C are illustrations of the laser intensity, and modulationwindows.

FIG. 6A is an illustration of the modulation intensity.

FIG. 6B is an illustration of the laser intensity and positions alongthe sampling window.

FIG. 7 is an illustration of a controller.

DESCRIPTION OF THE EMBODIMENTS

Embodiments will be described below with reference to the attacheddrawings. Further, an image photographing apparatus as disclosed in thefollowing can be applied to an object to be inspected such as an eye tobe inspected, skin, and internal organs.

Ophthalmoscope

A first embodiment is described with reference to of a fundus imagephotographing apparatus such as the photographing apparatus illustratedin FIG. 1.

Embodiments are directed towards systems, methods, and software whichare used in connection with an imaging system such as an ophthalmoscope.FIG. 1 is an illustration of an exemplary ophthalmoscope. Anophthalmoscope is a system or apparatus for obtaining information aboutan interior portion of the eye 111 (e.g., the fundus).

An exemplary embodiment may be a scanning ophthalmoscope. A scanningophthalmoscope scans a spot across the eye. The spot may be a spot oflight from a light source that is scanned across the eye.

In an exemplary embodiment, the spot of light is produced by a lightsource 101. The light source 101 may be incorporated into theophthalmoscope; alternatively, the ophthalmoscope may include an inputfor receiving a light source 101. The input for the light source 101 maybe a fiber optic input or a free space input. The light source 101 maybe a laser, a broadband light source, or multiple light sources. In anexemplary embodiment, the light source 101 is a super luminescent diode(SLD) light source having a wavelength of 840 nm. The wavelength of thelight source 101 is not particularly limited, but the wavelength of thelight source 101 for fundus image photographing is suitably set in arange of approximately 800 nm to 1,500 nm in order to reduce glare for aperson to be inspected and to maintain imaging resolution.

In one embodiment the light source is directly modulated by a modulationsignal 120. In an alternative embodiment, an external modulator 122 isused to modulate the light source. The external modulator may beincorporated into the light source 101 or may be connected to the lightsource via an optical fiber or free space optics.

In an exemplary embodiment, light emitted from the light source 101passes through a single-mode optical fiber 102, and is radiated ascollimated light (measuring light 105) by a collimator 103.

In an exemplary embodiment, the polarization of the irradiated light maybe adjusted by a polarization adjusting member 119 (not shown) providedin a path of the single-mode optical fiber 102. In an alternativeconfiguration of an exemplary embodiment, the light source 102 ispolarized and single-mode optical fiber 102 is polarization maintainfiber. In another configuration of an exemplary embodiment, thepolarization adjusting member may be placed after the collimator 103.Alternatively, the polarization adjusting member may be replaced with apolarizer.

The measuring light 105 radiated from the collimator 103 passes througha light division portion 104 including a beam splitter. An exemplaryembodiment may include an adaptive optical system. Exemplary embodimentsinclude both systems that do and do not include the adaptive opticalsystem.

The adaptive optical system includes a light division portion 106, awave front sensor 115, wave front correction device 108, and reflectivemirrors 107-1 to 107-4 for guiding the measuring light 105 to thosecomponents. The reflective mirrors 107-1 to 107-4 are provided to guidethe measuring light 105 to and from the pupil of an eye 111, the wavefront sensor 115, and the wave front correction device 108. The wavefront sensor 115 and the wave front correction 108 device may be in anoptically conjugate relationship. A beam splitter may be used as thelight division portion 106. The wave front sensor 115 may be aShack-Hartmann sensor.

The measuring light 105 passing through the light division portion 106is reflected on the reflective mirrors 107-1 and 107-2 to enter the wavefront correction device 108. The measuring light 105 reflected on thewave front correction device 108 and is further reflected on thereflective mirrors 107-3 and 107-4.

In an exemplary embodiment, one or two spatial phase modulatorsincluding a liquid crystal element is used as the wave front correctiondevice 108. The liquid crystal element may modulate a phase of only aspecific polarized component. In which case, two liquid crystal elementsmay be employed to modulate substantially orthogonal polarizedcomponents of the measuring light 105. In an alternative embodiment, thewave front correction device 108 is a deformable mirror.

The measuring light 105 reflected off mirror 107-4 is two-dimensionallyscanned by a scanning optical system 109. In an exemplary embodiment,the scanning optical system 109 includes a first scanner 109-1 and asecond scanner 109-2. The first scanner 109-1 rotates around the firstaxis, while the second scanner 109-2 rotates around a second axis. Thefirst axis is substantially orthogonal to the second axis.

FIG. 1 illustrates the first scanner 109-1 rotating in the x-y plane,while the second scanner 109-2 is rotating in the z-x plane. In thecontext of the present application, rotating the measuring light 105 ina first plane around the first axis is equivalent to rotating themeasuring light 105 in the first plane and is equivalent to scanning thespot of light in the main scanning direction or the lateral direction ofthe object being imaged. In the context of the present application,rotating the measuring light 105 in a second plane around the secondaxis is equivalent to rotating the measuring light 105 in the secondplane and is equivalent to scanning the spot of light in thesub-scanning direction or the longitudinal direction of the object beingimaged. The sub-scanning direction is substantially orthogonal to themain scanning direction.

A scanning period of the first scanner 109-1 is less than the scanningperiod of the second scanner 109-2. The order of the first scanner 109-1and the second scanner 109-2 may be exchanged without impacting theoperation of an exemplary embodiment. The first scanner 109-1 mayoperate in a resonant scanning mode.

In an exemplary embodiment, the scanning optical system 109 may be asingle scanning mirror that is rotated around the first axis by thefirst scanner 109-1 and around the second axis by the second scanner109-2 that is substantially orthogonal to the first axis. An exemplaryembodiment may also use non-mechanical beam steering techniques.

In an exemplary embodiment, the first scanner 109-1 and the secondscanner 109-2 are galvano-scanners. In another exemplary embodiment, oneof the first scanner 109-1 and the second scanner 109-2 is a resonantscanner. The resonant scanner may be used for the main scanningdirection. The resonant scanner may be tuned to oscillate at a specificfrequency.

The measuring light 105 scanned by the scanning optical system 109 isradiated to the eye 111 through eyepieces 110-1 and 110-2. The measuringlight radiated to the eye 111 is reflected, scattered, or absorbed onthe fundus. When the eyepieces 110-1 and 110-2 are adjusted in position,suitable irradiation may be performed in accordance with the diopter ofthe eye 111. Lenses may be used for the eyepiece portion in thisembodiment, but other optical components such as spherical mirrors mayalso be used.

Reflected light which is produced by reflection or scattering on aretina of the eye 111 then travels in the reverse direction along thesame path as in the case of incident light. A part of the reflectedlight is reflected by the light division portion 106 to the wave frontsensor 115 to be used for measuring a light beam wave front.

In an exemplary embodiment, a Shack-Hartmann sensor is used as the wavefront sensor 115. However, an exemplary embodiment is not limited to aShack-Hartmann sensor. Another wave front measurement unit, for example,a curvature sensor may be employed or a method of obtaining the wavefront by reverse calculation from the formed spot images may also beemployed.

In FIG. 1, when the reflected light passes through the light divisionportion 106, a part thereof is reflected on the light division portion104 and is guided to a light intensity sensor 114 through a collimator112 and an optical fiber 113. The light intensity sensor 114 convertsthe light into an electrical signal. The electrical signal is processedby a control unit 117 into an image of the object, and the image isdisplayed on a display 118.

The wave front sensor 115 is connected to an adaptive optics controlunit 116. The received wave front is transferred to the adaptive opticscontrol unit 116. The wave front correction device 108 is also connectedto the adaptive optics control unit 116 and performs modulation asinstructed by the adaptive optics control unit 116. The adaptive opticscontrol unit 116 calculates a modulation amount (correction amount) forcorrection to obtain wave front having no aberration based on the wavefront obtained by a measuring result of the wave front sensor 115, andinstructs the wave front correction device 108 to perform the modulationaccording to the modulation amount. The wave front measurement and theinstruction to the wave front correction device are repeated andfeedback control is performed so as to obtain a suitable wave front.

In an exemplary embodiment the light division portions 104 and 106 arefused fiber couplers. In an alternative exemplary embodiment, the lightdivision portions include partially reflective mirrors.

The detector 114 may detect reflections or fluorescence associated withthe scanning spot. The detection system may make use confocal microscopytechniques in which an aperture associated with the scanning spot isused to increase the resolution and/or contrast of the detection system.

Scanner

An exemplary embodiment is a scanning microscope such as a laserconfocal microscopes or a scanning laser ophthalmoscope (SLO). Thescanning microscope obtains a two dimensional image of a specimen usingtwo scanners 109-1 and 109-2 to dynamically update positions of a laserspot on the specimen. In an exemplary embodiment the two scanners are aresonant scanner 109-1 (fast scanner) and a linear scanner 109-2 (slowscanner). The fast scanner 109-1 is driven by a sinusoidal signal toachieve high-speed scanning hence its physical motion is also sinusoidalor very close to sinusoidal. The slow scanner is usually driven by aperiodic ramp signal or saw-tooth signal. The motion of the laser spotin the main scanning direction may be approximated with formula 1. Inwhich ω is the scanning frequency, A is the scaling factor, φ is thephase offset, and f(t) is the non-sinusoidal motion. The scanningposition as a function of time is illustrated in FIG. 2A.

x(t)=A sin(ωt+φ)+f(t)  (1)

Due to the sinusoidal effect, the speed of the fast scanner 109-1 at thecenter of the scanning area is much faster than that at the edge of thescanning area. The speed of the laser spot in the main scanningdirection may be approximated with formula 2. The scanning velocity as afunction of time is illustrated in FIG. 2B. The scanning velocity as afunction of scanning position is illustrated in FIG. 2C.

$\begin{matrix}{{v(t)} = {\frac{{x(t)}}{t} = {{A\; \omega \; {\cos \left( {{\omega t} + \varphi} \right)}} + {f^{\prime}(t)}}}} & (2)\end{matrix}$

When the laser output has uniform power over time, this sinusoidaleffect causes non-uniform distribution of laser energy across the fastscanning field of view (FOV), where a unit area at the two edgesreceives significantly more laser energy than a unit area at the centerdoes. The inventors have found that the intensity I(t) of the laser spotas it moves in the main scanning direction is approximately inverselyproportional to the velocity of the laser spot in the main scanningdirection as described in formula 3. FIG. 2D is an illustration of thelaser intensity of the laser spot as a function of the scanningposition, i.e., the distribution of laser energy across the field ofview.

$\begin{matrix}{{I(t)} \propto \frac{1}{v(t)}} & (3)\end{matrix}$

This issue dramatically limits the use of laser power on live subjects,e.g., live human eyes. Based on ANSI safety levels, the worst case hasto be considered before an experimental protocol is designed. In thisparticular case as shown in FIG. 2D, the edges of the specimen receiveapproximately 6 times the laser energy than the center. Therefore,researchers have to use a laser power that will be safe at the edges ofthe field of view, while unfortunately, the center only receives ⅙ ofthe laser energy that is received at the edges. This issue significantlyreduces signal to noise ratio (SNR) of the image since the SNR isproportional to laser energy or the photon number.

Prior art methods have employed an acoustic optical modulator (AOM) 122to mitigate this problem by blocking laser light to the subject's eyewhen the fast scanner is in the slow moving area. The AOM 122 can bemodulated to let light pass through only when the fast scanner is infast moving zone. Different implementations of this prior art methodallow 20%-35% of the laser light to be blocked by the AOM 122 when theresonant scanner is running in the 20%-35% slow motion zone. FIG. 3 isan illustration of this method, the shaded areas 302 are blocked by theAOM 122, while the area 304 is not blocked.

However, this prior art method does not take full advantage of the AOM122 in that, the distribution of laser energy in the fast motion zone isstill nonlinear where the new edge of the new field of view 304 receives1.5-2 times laser energy than the center. The light is turned ON/OFF (bythe AOM 122) dependent only on the motion of the fast scanner. Whileactually, about 5%-25% of the light is still delivered to the subjectwhen no data (image) is sampled due to back sweeping and jitter of theslow scanner.

The slow scanner 109-2 is usually driven by a low frequency ramp signal,e.g., 15-60 Hz, as illustrated in FIG. 4. Data in window 402 is notusable. When the slow scanner 109-2 runs backwards the image issignificantly compressed and is thus unusable. The first a few fastscanning lines of forward scanning of the slow scanner 109-2 areunusable due to jitter.

FIG. 5A is an illustration of the laser intensity experienced by aspecimen in two side by side scans. The black portion shows where thelaser spot intensity is the highest, and the white portion shows wherethe laser spot intensity is lowest. FIG. 5B is an illustration of howthe AOM 122 may be used in an ON/OFF mode to block laser light duringperiods 302 and 402 which are shown as semi-transparent gray blocks.Data sampling windows 502 are also illustrated in FIG. 5B.

In an exemplary embodiment, a new approach is introduced to do completelaser power modulation across the two-dimensional scanning field ofview. This approach allows the use of less laser power for the same SNR,or to achieve higher SNR while using the same laser power. The AOM 122may be used to modulate the laser power. In other embodiments, othermodulation tools may be used such as direct modulation, electro-opticmodulation, Electro-absorption modulation.

Inside the sampling windows 502, the laser power (i.e. the lightintensity) is modulated by a nonlinear curve 604 derived from equation 3as illustrated in FIG. 3. FIG. 6A is an illustration of the percent 602of the laser intensity that is modulated by the AOM 122 as a function ofposition. With uniform laser power, the energy distribution in equation3 as illustrated in FIG. 6B can also be written as a function ofposition as described in equation (4). In which x_(i) and x_(r) are twoboundaries of the valid data sampling window 502 in the fast scanningdirection as illustrated in FIG. 6B. The central location of the fastscanner x₀ is also illustrated in FIG. 6B.

I(x)=g(x)×ε[x _(i) ,x _(r)]  (4)

To achieve uniform laser energy on the specimen across the fast scanningFOV 502, the laser power should be modulated in accordance withmodulation pattern 602 illustrated in FIG. 6A. In an exemplaryembodiment, the modulation pattern may be based on Equation 5.

$\begin{matrix}{{P(x)} = {{\frac{{P\left( x_{0} \right)}{I\left( x_{0} \right)}}{I(x)}x} \in \left\lbrack {x_{i},x_{r}} \right\rbrack}} & (5)\end{matrix}$

In equation 5, P(x₀) is the laser power at the center of the fastscanning FOV, and P(x) is laser power elsewhere. This means that the twoedges will get less laser power and the center will get more.

In an exemplary embodiment, a Field Programming Gate Array (FPGA) withan analog-to-digital converter (ADC) and a digital-to-analog converter(DAC) can be used.

The ADC may be programmed by the FPGA to do image acquisition. The ADCreceives synchronization signals (H-sync and V-sync) from the twoscanners 109-1 and 109-2. The FPGA generates digitized H-sync and V-syncfor DAC and other FPGA applications. The ADC can work in master mode(with an internal phase locked pixel clock) or slave mode (with anexternal pixel clock). This pixel clock is used as the common pixelclock for the DAC.

In an exemplary embodiment, the DAC is programmed to generate an analogsignal to control the AOM, with the digitized H-sync, V-sync, and thecommon pixel clock from the ADC. These three clocks guarantee the DACoutput is synchronized with the motion of the two scanners.

The truncated data window 502 illustrated in FIG. 5B can be achieved byadding simple offsets to the DAC signal.

In an additional exemplary embodiment, the modulation of the laser powerdescribed by equation 5 includes additional pre-correction. The motionof the fast scanner is not linear in space domain. The laser power (notenergy) is sinusoidal across the fast scanning FOV, as described byequations (1)-(3).

Once the laser power modulation is applied in step 5, the raw image withsinusoidal distortion will have a bright center and dim edges acrossfasting scanning FOV. The reason for this is that each pixel on the rawimage has equal sampling time. Brightness of a pixel is determined byequation 6.

E=PΔt  (6)

Where E is the energy, P is the power, and Δt is the exposure time. Inone exemplary embodiment, Δt is the same for all pixels on the rawimage, but P is small at the two edges and large at the center. When theenergy E is used to calculate eye safety values Δt should be consideredthe same for all values. When the energy E is used to calculate theamount of energy detected at the detector, Δt may be based on the pixelclock. In one exemplary embodiment, the pixel clock is constant. In analternative exemplary embodiment, the pixel clock varies with position.

In one embodiment the raw image is corrected for sinusoidal distortions.However, the sinusoidal correction may be done using integration orinterpolation. To correct for sinusoidal distortion, in a unit area ofthe specimen, the edge areas need more raw pixels than the central areadoes.

Table 1 illustrates usage of laser power in three different mode ofoperation to achieve the same SNR.

TABLE 1 Laser power to achieve the same SNR Without modulation as in theprior art P(x_(O)) Simple modulation as in the prior art 0.25~0.4P(x_(O)) Complex modulation as disclosed herein 0.12~0.2 P(x_(O))

In general, the modulation curve is related to the velocity of the scan,as described in equation 6a.

M(t)=K(v(t))  (6a)

One example of this relationship is described below. In one exemplaryembodiment the modulation curve M(t) is inversely proportional to theaverage intensity at a point being illuminated on the sample asdescribed in equation (7) within a specific scanning window.

$\begin{matrix}{{M(t)} \propto \frac{1}{{\langle{I(t)}\rangle}_{\Delta \; t}} \propto {\langle{v(t)}\rangle}_{\Delta \; t}} & (7)\end{matrix}$

As stated in equation (3) the intensity is inversely proportional to thevelocity. The inventors have discovered that the modulation can beproportional the average velocity at the point being illuminated on thesample. Equation 8 describes how the modulation can also be written inintegral form.

$\begin{matrix}{{M(t)} \propto {\langle{v(t)}\rangle}_{\Delta \; t} \propto {\frac{1}{\Delta \; t}{\int_{t - \frac{\Delta \; t}{2}}^{t + \frac{\Delta \; t}{2}}{{v(t)}\ {t}}}}} & (8)\end{matrix}$

Equation (2) may be used to solve the integral in equation (8) so thatthe modulation can also be written in terms of the position of the spoton the sample as described in equation (9).

$\begin{matrix}{{{M(t)} \propto {\frac{1}{\Delta \; t}{\int_{t - \frac{\Delta \; t}{2}}^{t + \frac{\Delta \; t}{2}}{{v(t)}\ {t}}}} \propto {\frac{1}{\Delta \; t}{x(t)}}}_{t - \frac{\Delta \; t}{2}}^{t + \frac{\Delta \; t}{2}}} & (9)\end{matrix}$

The modulation curve may also be described over the entire field of viewusing Equation (10).

$\begin{matrix}{{{{M(t)} \propto {\frac{1}{\Delta \; t}{x(t)}}}_{t - \frac{\Delta \; t}{2}}^{t + \frac{\Delta \; t}{2}}{x \in \begin{bmatrix}{x_{i},} & x_{r}\end{bmatrix}}} = {{0\mspace{14mu} x} \notin \begin{bmatrix}{x_{i},} & x_{r}\end{bmatrix}}} & (10)\end{matrix}$

In addition, the intensity of the laser is not modulated at position x₀.A time t₀ may be defined in terms of x₀=x(t₀). In which x₀ is thecentral location of the fast scanner as illustrated in FIG. 6B. So thatequation 10 may be written more exactly as Equation (11).

$\begin{matrix}\begin{matrix}{{M(t)} = \frac{{\langle{v(t)}\rangle}_{\Delta \; t}}{{\langle{v\left( t_{0} \right)}\rangle}_{\Delta \; t}}} \\{= {{\frac{{x(t)}_{t - \frac{\Delta \; t}{2}}^{t + \frac{\Delta \; t}{2}}}{{x(t)}_{t_{0} - \frac{\Delta \; t}{2}}^{t_{0} + \frac{\Delta \; t}{2}}}x} \in \begin{bmatrix}{x_{i},} & x_{r}\end{bmatrix}}} \\{{{0\mspace{14mu} x} \notin \begin{bmatrix}{x_{i},} & x_{r}\end{bmatrix}}}\end{matrix} & (11)\end{matrix}$

An exemplary embodiment allows you to optimize the image quality even ifyou use non-even illumination for a laser scanning microscopy systemusing a resonant scanner. An exemplary embodiment will modulate lasernot only at on/off status, but also intensity of the laser power. Bymodulating laser intensity, the laser power can be accurately modulatedto a different level at different scanner locations. Spatial/temporalresolution of the modulation is limited by the pixel clock only, e.g.,tens of nanoseconds or less than one micrometer, and the accuracy of thelaser power is limited by the resolution of digital to analog device. Anexemplary embodiment will reduce of the use of laser power to thesubject at least 50% compared to the existing technologies, or thesignal-to-noise ratio (SNR) of the image will be increased by at least afactor of 2 when the same laser power is used.

FIG. 7 is an illustration of a device 117 that may be used to implementan exemplary embodiment. The device 117 may be a personal computer or acustom built computing device. The device 117 includes a centralprocessing unit (CPU) 702 for executing instructions. The instructionsmay be encoded on a non-transitory computer readable medium. Thenon-transitory computer readable medium may include a recording medium,such as a hard disk, a floppy disk, an optical disk, a magnetic disk, amagneto-optical disk, a magnetic tape, and a non-volatile memory card,and a drive for driving the recording medium and recording informationin it. The instructions and the data on which the instructions areperformed may be stored in a memory 704. The device may include an inputdevice 706 such as a keyboard, a mouse, touch panel, a stylus, and/orone or more buttons which provides a user with a method for providinginformation to the device. A bus 708 includes an address bus or a databus and is connected to each unit in the configuration. The device 117may include or be connected to a display device 118. The display device118 can be used to display the state of the device and/or various inputoperations and processing results. The display device 118 can be formedof an LCD (liquid crystal display), a PDP (plasma display panel), anOLED (organic light-emitting diode), or the like, and can display imagesand/or text. The device 117 may include or be connected to a framegrabber 712 that is connected to detector 114.

Aspects of exemplary embodiment can also be realized by a computer of asystem or apparatus (or devices such as a CPU or MPU) that reads out andexecutes a program recorded on a memory device to perform the functionsof the above-described embodiments, and by a method, the steps of whichare performed by a computer of a system or apparatus by, for example,reading out and executing a program recorded on a memory device toperform the functions of the above-described embodiments. For thispurpose, the program is provided to the computer for example via anetwork or from a recording medium of various types serving as thememory device (e.g., computer-readable medium). In such a case, thesystem or apparatus, and the recording medium where the program isstored, are included as being within the scope of an exemplaryembodiment.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

What is claimed is:
 1. An imaging system for imaging an object,comprising: a scanner, wherein the scanner positions a spot of lightfrom a light source on the object along a scanning path, the scanningpath includes a plurality of scan lines, wherein the spot moves alongthe scanning path at a scanning velocity, wherein the scanning velocityis not constant; a detector arranged to output data associated withpositions along the scanning path; and one or more processors thatperform calculations comprising: calculating pixels based on the outputdata; and constructing an image of the object based on the pixels;wherein, intensity of the spot of light is modulated as a function ofthe scanning velocity.
 2. The imaging system of claim 1, furthercomprising an external modulator for modulating the light source.
 3. Theimaging system of claim 1, wherein the light source is directlymodulated.
 4. The imaging system of claim 1, further comprisingcalculating the pixels by integrating the intensity of the detectedlight.
 5. The imaging system of claim 1, wherein the intensity of thespot of light is modulated as a function of the average scanningvelocity.
 6. The imaging system of claim 5, wherein the average scanningvelocity is averaged over a period equal to the pixel clock time.
 7. Theimaging system of claim 1, wherein the intensity of the spot of light ismodulated as function of the scanning velocity during a first window,and the intensity of the spot of light is substantially zero outside ofthe first window.
 8. The imaging system of claim 1, wherein the scanneris a resonant scanner that positions the spot of light with sinusoidalmotion; and wherein constructing the image further comprises correctingimage distortion caused by the sinusoidal motion by integration.
 9. Animaging method for imaging an object, comprising: scanning a spot oflight from a light source on the object along a scanning path, thescanning path includes a plurality of scan lines, wherein the spot movesalong the scanning path at a scanning velocity, wherein the scanningvelocity is not constant; modulating intensity of the spot of light as afunction of the scanning velocity; detecting output data associated withpositions along the scanning path; calculating pixels based on theoutput data; and constructing an image of the object based on thepixels.
 10. A non-transitory computer readable medium encoded withinstructions for imaging an object, comprising: sending instructions toa scanner to scan a spot of light from a light source on the objectalong a scanning path, the scanning path includes a plurality of scanlines, wherein the spot moves along the scanning path at a scanningvelocity, wherein the scanning velocity is not constant; sendinginstructions to modulate intensity of the spot of light as a function ofthe scanning velocity; receiving output data from a detector, the outputdata associated with positions along the scanning path; calculatingpixels based on the output data; and constructing an image of the objectbased on the pixels.